o rte can now contain a pointer to both cached and uncached rta. Protocols
which don't need their own attribute caching can now just fill-in a rta,
link it to rte without any calls to attribute cache and call rte_update()
which will replace rte->attrs by a cached copy.
o In order to support this, one of previously pad bytes in struct rta
now holds new attribute flags (RTAF_CACHED). If you call rte_update()
with uncached rta, you _must_ clear these flags. In other cases rta_lookup()
sets it appropriately.
o Added rte_free() which is useful when you construct a rte and then the
circumstances change and you decide not to use it for an update. (Needed
for temporary rte's in kernel syncer...)
protocol callbacks for route insertion and deletion from the central table.
RIP should maintain its own per-protocol queue of existing routes, scan it
periodically and call rte_discard() for routes that have timed out.
loop detection. This is needed since both RIP and OSPF handle multiple
neighbors and they need to redistribute routes learned from each neighbor
to the remaining ones.
protocols and don't send route/interface updates to them and when they come up,
we resend the whole route/interface tables privately.
Removed the "scan interface list after protocol start" work-around.
